Above you see many horizontal black stripes and two vertical green striped bars.
Do the blue bars have identical luminance? They certainly differ in perceived brightness.
Grab the slider with the mouse and observe the startling change in brightness when the black grating is moved away from the green bars.

You can try to match the two greenish colours with the black grid in place – I find it very difficult to match them. You can also change the large black grating to some other colour: for instance a slightly darkende green: the effect is still there.

Comment

Lateral inhibition predicts the opposite effect, so the mechanism must be quite different. See Corney & Lotto (2007) for a promising new explanation approach. White (1979, 1981) described these luminance effects, called White's illusion or Munker-White illusion. When the horizontal stripes differ in color (not black/white as here), strong color shifts result, the Munker illusion.

Sources

Anderson BL (1997) A theory of illusory lightness and transparency in monocular and binocular images: the role of contour junctions. Perception 26:419–453

Corney D, Lotto RB (2007) What Are Lightness Illusions and Why Do We See Them? PLoS Comput Biol 3:e180
This interesting paper shows that this illusion “automatically” occurs as a by-product when an artificial neural network is trained for brightness constancy.